Salts comprising cyanoborate anions

ABSTRACT

A process for the preparation of alkali metal cyanoborates, the further conversion thereof into salts comprising cyanoborate anions and organic cations, these salts, and the use thereof as ionic liquids are described.

The present invention relates to a process for the preparation of alkalimetal cyanoborates, to the further conversion thereof into saltscomprising cyanoborate anions and organic cations, to these salts, andto the use thereof as ionic liquids.

Ionic liquids or liquid salts are ionic species which consist of anorganic cation and a generally inorganic anion. They do not containneutral molecules, and generally have melting points below 373 K. Amultiplicity of compounds which are used as ionic liquids are known inthe prior art. In particular, they are also the subject-matter of aseries of patents and patent applications.

Thus, solvent-free ionic liquids were disclosed for the first time byHurley and Wier in a series of US patents (U.S. Pat. Nos. 2,446,331,2,446,339 and 2,446,350). These “salts which are molten at roomtemperature” comprised AlCl₃ and a multiplicity of n-alkylpyridiniumhalides.

In recent years, some review articles have been published on this topic(R. Sheldon “Catalytic reactions in ionic liquids”, Chem. Commun., 2001,2399-2407; M. J. Earle, K. R. Seddon “Ionic liquids. Green solvent forthe future”, Pure Appl. Chem., 72 (2000), 1391-1398; P. Wasserscheid, W.Keim “Ionische Flüssigkeiten—neue Lösungen für dieÜbergangsmetallkatalyse” [Ionic Liquids—Novel Solutions forTransition-Metal Catalysis], Angew. Chem., 112 (2000), 3926-3945; T.Welton “Room temperature ionic liquids. Solvents for synthesis andcatalysis”, Chem. Rev., 92 (1999), 2071-2083; R. Hagiwara, Ya. Ito “Roomtemperature ionic liquids of alkylimidazolium cations and fluoroanions”,Journal of Fluorine Chem., 105 (2000), 221-227).

The properties of ionic liquids, for example melting point, thermal andelectrochemical stability, viscosity, are greatly influenced by thenature of the anion. By contrast, the polarity and hydrophilicity orlipophilicity can be varied through a suitable choice of thecation/anion pair. There is therefore a basic demand for novel ionicliquids having varied properties which facilitate additionalpossibilities with respect to their use.

Crucial advances in the area of ionic liquids have been achieved withthe discovery of 1-ethyl-3-methylimidazolium chloroaluminate. This salthas a broad liquid range and an electrochemical window of greater than 3V and is thus of great interest for electrochemical and syntheticpurposes. However, its use is limited by the chemical instability,especially to moisture. After the discovery of the morehydrolysis-stable 1-ethyl-3-methylimidazolium tetrafluoroborate,combinations of alkylimidazolium cations with inorganic or organicanions were investigated, of which 1-ethyl-3-methylimidazoliumtetrafluoroborate is the best characterised.

The stability of the imidazolium cation is relatively high and itsdecomposition temperature is essentially determined by the anion. Thus,1-ethyl-3-methylimidazolium salts with triflate andbis(trifluoromethylsulfonyl)imide anions are stable up to 400° C.,whereas 1-ethyl-3-methylimidazolium tetrafluoroborate is only stable upto 300° C.

The prior art describes borate anions in which fluorine ligands havebeen replaced by cyanide (E. Bernhardt, G. Henkel, H. Willner, Z. Anorg.Allg. Chem. 626 (2000) 560; D. Williams, B. Pleune, J. Kouvetakis, M. D.Williams, R. A. Andersen, J. Amer. Chem. Soc. 122 (2000) 7735; E.Bernhardt, M. Berkei, M. Schürmann, H. Willner, Z. Anorg. Allg. Chem.628 (2002) 1734) and trifluoromethyl ligands (E. Bernhardt, G. Henkel,H. Willner, G. Pawelke, H. Bürger, Chem. Eur. J. 7 (2001) 4696; G.Pawelke, H. Bürger, Coord. Chem. Rev. 215 (2001) 243). Thetrifluoromethyl borates are synthesised here starting from thecyanoborates, but the cyanoborates are only accessible with difficultyand in small amounts. The synthesis of [B(CN₄)]⁻ is labour-intensive andcan only be carried out on a small preparative scale. In addition, thestarting materials are expensive.

The object of the present invention is to provide novel stable compoundshaving valuable properties which can be used as ionic liquids, and aprocess for the preparation thereof. In particular, the object is toprovide salts with borate anions which have higher stability than thesalts with tetrafluoroborate anions.

A further object of the present invention is to provide an effective andeconomical process for the preparation of these borate salts and theirprecursors.

This object is achieved in accordance with the invention by thecharacterising features of the main claim and the sub-claims.

The present invention therefore relates firstly to a process for thepreparation of alkali metal cyanoborates of the general formula (1)M⁺[B(CN)₄]⁻  (1),where M is selected from the group Li, Na, K, Rb and Cs,in which the readily available starting substances alkali metaltetrafluoroborate M[BF₄] (M=Li, Na, K, Rb, Cs) and alkali metal cyanideMCN (M=Li, Na, K, Rb, Cs) are reacted with one another in a solid-statereaction.

The alkali metal tetrafluoroborate used in accordance with the inventionis preferably potassium tetrafluoroborate K[BF₄] or sodiumtetrafluoroborate Na[BF₄], and the alkali metal cyanide used inaccordance with the invention is preferably potassium cyanide KCN orsodium cyanide NaCN.

In a preferred variant of the process according to the invention, thealkali metal tetrafluoroborate is reacted with the alkali metal cyanidein the presence of a lithium halide. The lithium halide here is selectedfrom LiCl, LiBr and LiI, it is particularly preferably lithium chlorideLiCl.

Alkali metal cyanide and lithium halide can in each case be employed inan excess of one of the two reagents. However, the alkali metal cyanideand the lithium halide are preferably brought to reaction inapproximately in the molar ratio 1:1.

The alkali metal tetrafluoroborate and the alkali metal cyanide arepreferably employed in the molar ratio of 1:4 to 1:12, particularlypreferably in the molar ratio of about 1:9.

The alkali metal tetrafluoroborate:alkali metal cyanide:lithium halidemolar ratio of about 1:9:9 is therefore very particularly preferablyused.

The starting materials used for the reaction according to the inventionare particularly preferably potassium tetrafluoroborate K[BF₄] as alkalimetal tetrafluoroborate and potassium cyanide KCN as alkali metalcyanide.

The solid-state reaction according to the invention is carried out attemperatures between 100° C. and 500° C. Preference is given totemperatures of 250 to 400° C., particularly preferably 280-340° C.

Without restricting generality, the subject-matter of the solid-statereaction according to the invention is explained with reference to ageneral example: K[BF₄], KCN and LiCl are mixed in the molar ratio of1:9:9 and subsequently brought to reaction in the melt. The reactiontemperature is selected in such a way that on the one hand the KCN/LiClmixture forms a eutectic melting at 270-290° C. and on the other handthe tetracyanoborate salts formed only decompose slowly (<400-500° C.).Evaluation of powder diffractograms of the cooled melt of KCN with LiCl(molar ratio 1:1) enables mixed crystals of the K(Cl,CN) type (a=6.34 Å,F m3m) and a further unidentified compound (d=4.958, 2.878, 2.728,2.482, 2.175 Å) to be detected. The yield of K[B(CN)₄] is virtuallytemperature-independent in the range 280-340° C. and is about 40-60%,based on K[BF₄]. It is found in further experiments that a reduction inthe molar ratio of K[BF₄] to KCN/LiCl from 1:9 to 1:4.5 results inreductions in yield. The Raman spectra of the reaction mixtures showthat the tetracyanoborate is in the form of the lithium salt after thereaction (v(CN)=2263 cm⁻¹).

In the analogous reaction using an NaCN/LiCl mixture, mixed crystals ofthe (Li,Na)(Cl,CN) type (a=5.50 Å Fm3m) form in the melt of NaCN withLiCl (molar ratio 1:1) besides a little LiCN (d=5.216, 3.626 Å, m.p.160° C.). A eutectic (120-140° C.) forms between NaCN with LiCl, incontrast to KCN/LiCl, but the mixed crystals only melt at 360-540° C.;this is probably the cause of the lower yields (about 25%) ofNa[B(CN)₄].

During work-up of the reaction products, the excess cyanide must firstlybe destroyed. It is found that oxidation of the cyanide using aqueous30% H₂O₂ solution is the best work-up method. The low salt burden andthe complete and rapid degradation of the cyanide remaining in thereaction mixture, as well as the good yields outweigh the singledisadvantage, the often vigorous and difficult-to-control reaction ofthe cyanide. The tetracyanoborate is subsequently extracted from theaqueous solution and converted into the K or Na salt by re-extraction.

An alternative method available for the work-up of the solid-statereaction products is oxidation of the unreacted cyanide using aqueousNaOCl solution, which proceeds within a few minutes under very mildconditions, i.e. without warming or foaming of the reaction mixture. Thework-up is then carried out analogously to that with H₂O₂. However, thisfurther work-up is more labour-intensive and time-consuming owing to thegreater salt burden.

The present invention furthermore relates to a process for thepreparation of alkali metal cyanoborates of the general formula (2)M⁺[BF_(n)(CN)_(4-n)]⁻  (2),where n=0, 1, 2 or 3 andM is selected from the group Li, Na, K, Rb and Cs,in which an alkali metal cyanide MCN, where M=Li, Na, K, Rb, Cs, isreacted with boron trifluoride etherate BF₃.OEt₂.

On use of coarse-grained potassium cyanide KCN and BF₃.OEt₂, equimolaramounts of K[BF₄] and K[BF₂(CN)₂] also form in the reaction according tothe invention alongside the primary adduct K[BF₃(CN)], in accordancewith the following equations:

In addition, the two salts K[BF(CN)₃] and K[B(CN)₄] form to a lesserextent, the former in particular if the reaction mixture is held attemperatures above room temperature.

In accordance with the invention, the boron trifluoride etherate isreacted with the alkali metal cyanide in the presence of an aproticsolvent. Without restricting generality, the aprotic solvent can be, forexample, acetonitrile, diethyl ether, tetra-hydrofuran and/ordimethoxyethane.

The alkali metal cyanide used for the process according to the inventionis preferably potassium cyanide KCN.

The starting materials are preferably reacted in accordance with theinvention at temperatures of −80 to 100° C., particularly preferably atroom temperature.

Volatile by-products which are removed under reduced pressure may beformed during the reaction. Mostly, however, by-products which areinsoluble in the solvents used and are separated off by filtration form.The solvent is, if desired, removed under reduced pressure together withvolatile by-products, and the alkali metal cyanoborates obtained can, ifdesired, be separated and purified by a common possibility known to theperson skilled in the art.

A third and fourth subject-matter of the present invention are a processfor the preparation of salts with cyanoborate anions of the generalformula (3) and the corresponding salts of the general formula (3)Kt⁺[BF_(n)(CN)_(4−n)]⁻  (3),where n=0, 1, 2 or 3, and Kt⁺ is an organic cation, with the provisothat the cation Kt⁺ is not [N(C₄H₉)₄]⁺ for n=0.

For the preparation of the salts, an alkali metal cyanoborate of thegeneral formula M⁺[B(CN)₄]⁻, where M is selected from the group Li, Na,K, Rb and Cs, or an alkali metal cyanoborate of the general formulaM⁺[BF_(n)(CN)_(4−n)]⁻, where n=0, 1, 2 or 3 and M is selected from thegroup Li, Na, K, Rb and Cs, is reacted with Kt⁺X⁻, where X is a halogenselected from Cl, Br and I, and Kt⁺ is an organic cation, with theproviso that the cation Kt⁺ is not [N(C₄H₉)₄]⁺ for n=0.

The organic cation Kt⁺ is preferably selected from the group

-   -   where R=H, with the proviso that at least one R on the hetero        atom is different from H,        -   straight-chain or branched alkyl having 1-20 carbon atoms        -   straight-chain or branched alkenyl having 2-20 carbon atoms            and one or more double bonds        -   straight-chain or branched alkynyl having 2-20 carbon atoms            and one or more triple bonds        -   saturated, partially or fully unsaturated cycloalkyl having            3-7 carbon atoms        -   halogen, in particular fluorine or chlorine, with the            proviso that no halogen-hetero atom bond is present,        -   —NO₂, with the proviso that no bond to a positively charged            hetero atom is present, and at least one R is different from            NO₂,        -   —CN, with the proviso that no bond to a positively charged            hetero atom is present, and at least one R is different from            CN,        -   where the R are in each case identical or different,        -   where the R may be bonded to one another in pairs by single            or double bond,        -   where one or more R may be partially or fully substituted by            halogens, in particular —F and/or —Cl, or partially by —CN            or —NO₂, with the proviso that not all R are fully            halogenated,        -   and where one or two carbon atoms of the R may be replaced            by hetero atoms and/or atom groups selected from the group            —O—, —C(O)—, C(O)O—, —S—, —S(O)—, —SO₂—, —S(O)₂O—, —N═, —P═,            —NR′—, —PR′—, —P(O)(OR′)—, —P(O)(OR′)O—, —P(O)(NR′R′)—,            —P(O)(NR′R′)O—, —P(O)(NR′R′)NR′—, —S(O)NR′— and —S(O)₂NR′—,            where R′=H, non-, partially or perfluorinated C₁- to            C₆-alkyl or non-, partially or perfluorinated phenyl.

For the purposes of the present invention, fully unsaturatedsubstituents are also taken to mean aromatic substituents.

Besides hydrogen, suitable substituents R of the organic cation inaccordance with the invention are: C₁- to C₂₀—, in particular C₁- toC₁₂-alkyl groups, C₂— to C₂₀—, in particular C₂— to C₁₂—, alkenyl oralkynyl groups, saturated or unsaturated, i.e. also aromatic, C₃- toC₇-cycloalkyl groups, NO₂, CN or halogens. However, a restricting factorfor the halogens here is that they only occur as substituents on carbonatoms, but not on hetero atoms. NO₂ and CN do not occur as substituentsof a positively charged hetero atom; furthermore, not all substituentssimultaneously have the meaning of NO₂ or CN.

The substituents R may also be bonded in pairs in such a way thatcyclic, bi- or polycyclic cations are formed. The substituents may bepartially or fully substituted by halogen atoms, in particular by Fand/or Cl, or partially by CN or NO₂ and contain one or two hetero atomsor atom groups, selected from the group 0, (O), C(O)O, S, S(O), SO₂,SO₂O, N, P, NH, PH, NR′, PR′, P(O)(OR′), P(O)(OR′)O, P(O)(NR′R′),P(O)(NR′R′)O, P(O)(NR′R′)NR′, S(O)NR′ and S(O)₂NR′. In the case ofcomplete halogenation, however, not all substituents R present may befully halogenated, i.e. at least one R is not perhalogenated.

Without restricting generality, examples of substituents according tothe invention of the organic cation are:

—F, —Cl, —Br, —I, —CH₃, —C₂H₅, —C₃H₇, —CH(CH₃)₂, —C₄H₉, —C(CH₃)₃,—C₅H₁₁, —C₆H₁₃, —C₆H₁₃, —C₇H₁₅, —C₈H₁₇, —C₉H₁₉, —C₁₀H₂₁, —C₁₂H₂₅,—C₂₀H₄₁, —OCH₃, —OCH(CH₃)₂, CH₂OCH₃, —C₂H₄OCH(CH₃)₂, —SCH₃, —SCH(CH₃)₂,—C₂H₄C₂H₅, —C₂H₄SCH(CH₃)₂, —S(O)CH₃, —SO₂CH₃, —SO₂C₂H₅, —SO₂C₃H₇,—SO₂CH(CH₃)₂, —CH₂SO₂CH₃, —OSO₂CH₃, —OSO₂CF₃, —CH₂N(H)C₂H₅,—C₂H₄N(H)C₂H₅, —CH₂N(CH₃)CH₃, —C₂H₄N(CH₃)CH₃, —N(CH₃)₂, —N(CH₃)C₃H₅,—N(CH₃)CF₃, O—C₄H₈—O—C₄H₉, —S—C₂H₄—N(C₄H₉)₂, —OCF₃, —S(O)CF₃, —SO₂CF₃,—CF₃, —C₂F₅, —C₃F₇, —C₄F₉, —C(CF₃)₃, —CF₂SO₂CF₃, —C₂F₄N(C₂F₅)C₂F₅,—CF═CF₂, —C(CF₃)═CFCF₃, —CF₂CF═CFCF₃, —CF═CFN(CF₃)CF₃, —CFH₂, —CHF₂,—CH₂CF₃, —C₂F₂H₃, —C₃H₆, —CH₂C₃F₇, —C(CFH₂)₃, —CHO, —C(O)OH, —CH₂C(O)OH,—CH₂C(O)CH₃, —CH₂C(O)C₂H₅, —CH₂C(O)OCH₃, CH₂C(O)OC₂H₅, —C(O)CH₃,—C(O)OCH₃,

Without restricting generality, the following organic cations areparticularly preferred as salts according to the invention:

The salts according to the invention are advantageously very readilysoluble in organic solvents. In comparison to known liquid salts, thesalts according to the invention surprisingly have low viscosity. Thesalts according to the invention are advantageously stable. They can beisolated and stored at room temperature. Furthermore, the saltsaccording to the invention are relatively easy to prepare, and readilyavailable starting materials are required.

All compounds according to the invention and compounds of the formula[N(C₄H₉)₄]⁺[B(CN)₄]⁻ have a salt-like character, relatively low meltingpoints (usually below 100° C.) and can be used as ionic liquids.

The salts according to the invention and salts of the formula[N(C₄H₉)₄]⁺[B(CN)₄]⁻ can be employed as solvents for many synthetic orcatalytic reactions, for example Friedel-Crafts acylation andalkylation, Diels-Alder cycloadditions, hydrogenation and oxidationreactions, Heck reactions. Furthermore, for example, fluorinatedsolvents for secondary and primary batteries can be synthesised.

The salts according to the invention and salts of the formula[N(C₄H₉)₄]⁺[B(CN)₄]⁻ are suitable as precursors for the preparation ofliquid-crystal compounds and of active ingredients, inter alia formedicaments and crop-protection agents.

It is also possible to use the compounds according to the invention andthe salts of the formula [N(C₄H₉)₄]⁺[B(CN)₄]⁻ as non-aqueouselectrolyte, optionally in combination with other electrolytes known tothe person skilled in the art.

In addition, the salts according to the invention and salts of theformula [N(C₄H₉)₄]⁺[B(CN)₄]⁻ are of interest as non-aqueous, polarsubstances in suitable reactions as phase-transfer catalyst or as mediumfor the heterogenisation of homogeneous catalysts.

The complete disclosure content of all applications, patents andpublications mentioned above and below are incorporated into thisapplication by way of reference.

Even without further comments, it is assumed that a person skilled inthe art will be able to utilise the above description in the broadestscope. The preferred embodiments and examples should therefore merely beregarded as descriptive disclosure which is absolutely not limiting inany way.

The NMR spectra were measured on solutions in deuterated solvents at 20°C. in a Bruker Avance DRX-300 spectrometer with a 5 mm ¹H/BB broad-bandhead with deuterium lock. The measurement frequencies of the variousnuclei are: ¹H: 300.13 MHz, ¹¹B: 96.92 MHz, ¹³C, 75.47 MHz, ¹⁹F: 282.41MHz and ¹⁵N: 30.41 MHz. The referencing method is indicated separatelyfor each spectrum or each data set.

DSC measurements were carried out in a Netzsch DSC 204 instrument. Thetemperature and sensitivity were calibrated using naphthalene, benzoicacid, KNO₃, AgNO₃, LiNO₃ and CsCl. In each case, 5-20 mg of thesubstances were weighed out into an aluminium crucible and sealed withaluminium caps with a small aperture. The investigation was carried outin the temperature range from 25 to 500° C. Unless indicated otherwise,the heating rate is 10 Kmin⁻¹. During the measurement, the sample spacewas flushed with dry nitrogen. The samples of air-sensitive substanceswere prepared in a dry box and transported to the analytical instrumentin an argon-filled vial. The data evaluation was carried out using theNetzsch Protens 4.0 program.

The elemental analyses were carried out by the microanalysis combustionmethods using a Euro EA3000 from HEKA-Tech GmbH. The samples ofair-sensitive substances were prepared in a dry box and transported tothe analytical instrument in an argon-filled vial. The error limits forthe recorded atoms are: C: ±0.3%, H: ±0.1%, N: ±0.2%.

EXAMPLE 1 Synthesis of K[B(CN)₄]

KCN, LiCl and K[BF₄] are ground coarsely and mixed with one another in amortar in a dry box (MBraun, Munich). The mixture is finely ground usinga commercially available coffee grinder. The reaction mixture issubsequently transferred into a nickel crucible (Ø_(internal)=101 mm,d_(wall)=2 mm, h=85 mm). The crucible is covered loosely by an iron lid,transferred from the dry box into a muffle furnace (VMK 93, KontronMaterial und Strukturanalyse GmbH) and heated. When the reaction iscomplete, the crucible with the metal cover is removed from thestill-hot muffle furnace and cooled to room temperature in air.

The cooled grey/black porous reaction mixture is transferred out of thecrucible into a mortar and crushed coarsely. 150 ml of water aresubsequently added to the comminuted solid in a 3 l beaker, and a totalof 350 ml of H₂O₂ (30% aqueous solution, about 3 mol) are added inapproximately 30 ml portions over a period of half an hour with constantstirring. The reaction, which commences exothermically with vigorousevolution of gas, is controlled by addition of ice. The reaction mixture(V=2.3 l) is divided between two 31 beakers and acidified usingconcentrated HCl (about 300 ml, about 3.6 mol) (pH 5-7) until gasevolution is no longer observed. It is subsequently checked whethercyanide residues are still present in the mixture (cyanide test, MerckKGaA, Darmstadt, Germany). The mixture is then filtered, and 28 ml (0.34mol) of conc. HCl are added to the yellow solution with stirring. 47 g(63 ml, 0.33 mol) of tripropylamine are subsequently added. The reactionmixture is stirred for 15 minutes and extracted with dichloromethane(250, 150 and 50 ml). The combined organic phases are washed with 200 mlof H₂O, and the washings are re-extracted with 25 ml of dichloromethane.The combined dichloromethane phases are dried over MgSO₄ and filteredthrough a glass frit (D4). 35 g (0.63 mol) of KOH are dissolved in alittle water and added to the organic solution with vigorous stirring. Abeige oily substance immediately precipitates out and forms lumps on thevessel base after further stirring (30 min). Thedichloromethane/tripropylamine mixture is decanted off, and the productis extracted from the residue with THF (200, 100 and 50 ml). Thecollected THF phases are dried using K₂CO₃, and finally all volatileconstituents are removed in a rotary evaporator. The white product iswashed with dichloromethane and dried at room temperature under reducedpressure.

TABLE 1 Synthesis of K[B(CN)₄] Temp. Time K[BF₄] KCN LiCl K[B(CN)₄]Yield ° C. hrs g mol G mol g mol g mol % 300 1.5 37.2 0.30 170.3 2.62116.1 2.74 29.2 ^([a]) 0.19 64 340 0.75 36.9 0.29 170.0 2.61 116.2 2.7427.0 ^([a]) 0.18 60 340 1.25 36.9 0.29 169.9 2.61 115.9 2.74 26.7 ^([a])0.17 59 340 2 37.0 0.29 160.6 2.47 115.9 2.74 20.8 ^([a]) 0.14 46 340 336.7 0.29 172.5 2.65 102.8 2.42 20.3 ^([b]) 0.13 45 340 3 36.8 0.29160.1 2.46 115.2 2.72 18.8 ^([a]) 0.12 42 340 3 36.7 0.29 180.9 2.78104.7 2.46 17.4 ^([a]) 0.11 39 ^([a]) Oxidation of the unreacted CN⁻using H₂O₂. ^([b]) Oxidation of the unreacted CN⁻ using NaOCl.

¹³C{¹H}-NMR: δ=123.3 ppm (q, 4C, CN), ¹Δ¹³C(^(10/11)B)=0.0021 ppm,¹J(¹¹B,¹³C)=70.9 Hz; ¹¹B-NMR: δ=−38.6 ppm, ¹J(¹¹B,¹³C)=71.2 Hz; solvent:CD₃CN reference substances: ¹³C-NMR solvent peak (against TMS) and¹¹B-NMR BF₃.Et₂O/CD₃CN as external standard.

The NMR data are identical with those in the prior art (E. Bernhardt, G.Henkel, H. Willner, Z. Anorg. Allg. Chem. 626 (2000) 560).

Results of the Elemental Analysis:

C [%] H [%] N [%] theoretical 31.20 — 36.39 found 31.35 — 35.97

According to DSC measurements, the salt decomposes above 450° C.

EXAMPLE 2 Synthesis of Na[B(CN)₄]

170.3 g (2.62 mol) of KCN, 116.1 g (2.74 mol) of LiCl and 37.2 g (0.30mol) of K[BF₄] are weighed out, ground coarsely in a mortar and mixedwith one another. The further procedure corresponds to that describedunder Example 1 (reaction temperature 300° C., reaction time 1.5 hours)as far as the obtaining of the dichloromethane extract.

2 equivalents of NaOH (about 25 g, 0.63 mol) are dissolved in as littlewater as possible (about 10-20 ml) and added dropwise to the organicsolution with vigorous stirring. A beige oily substance immediatelyprecipitates out and forms lumps on the vessel base after furtherstirring (at least 30 min). The dichloromethane/tripropylamine mixtureis decanted off, and the product is extracted from the residue with THF(200 ml, 100 ml and 50 ml). If the beige residue becomes liquid due tothe extraction, its viscous consistency can be restored by carefuladdition of Na₂CO₃ or Na₂SO₄.

The collected THF phases are dried using Na₂CO₃ or Na₂SO₄, and finallyall volatile constituents are removed in a rotary evaporator. The whiteproduct is washed with dichloromethane in order to remove amine residuesand dried at 60° C. under reduced pressure. Yield 25.3 g (62%, 0.18mol).

¹³C{¹H}-NMR: δ=123.3 ppm (q, 4C, CN), ¹Δ¹³C(^(10/11)B)=0.0021 ppm,¹J(¹¹B,¹³C)=70.9 Hz; ¹¹B-NMR: δ=−38.6 ppm, ¹J(¹¹B,¹³C)=71.2 Hz; solvent:CD₃CN reference substances: ¹³C-NMR solvent peak (against TMS) and¹¹B-NMR BF₃.Et₂O/CD₃CN as external standard

The NMR data are identical with those in the prior art (E. Bernhardt, G.Henkel, H. Willner, Z. Anorg. Allg. Chem. 626 (2000) 560).

Results of the Elemental Analysis:

C [%] H [%] N [%] theoretical 34.85 — 40.64 found 34.60 — 40.15

EXAMPLE 3 Lithium Tetracyanoborate, Li[B(CN)₄]

5 g (32 mmol) of K[B(CN)₄] are dissolved in 20 ml of water and reactedwith 8 ml of 37% hydrochloric acid (96 mmol) and 8 ml of ^(n)Pr₃N (42mmol). This mixture is then extracted twice with 50 ml of CH₂Cl₂ eachtime, the organic phase is dried using MgSO₄, and a solution of 3 g ofLiOH.H₂O (72 mmol) in 20 ml of water is added, and the mixture isstirred vigorously for one hour. All volatile products are removed underreduced pressure. Li[B(CN)₄] is extracted from the residue with 50 ml ofCH₃CN in a Soxlett apparatus. The organic phase is evaporated in arotary evaporator. The crude product is recrystallised from water,washed with 50 ml of CH₂Cl₂ and freed from solvent residues underreduced pressure. Yield 3.5 g (80%, 29 mmol).

According to DSC measurements, the salt decomposes above 470° C.

EXAMPLE 4 Ammonium Tetracyanoborate, NH₄[B(CN)₄]

0.31 g (2.0 mmol) of K[B(CN)₄] are dissolved in 8 ml of water, thenreacted with a solution of 0.20 g (1.1 mmol) of (NH₄)₂[SiF₆] in 8 ml ofwater. All volatile constituents are removed under reduced pressure.NH₄[B(CN)₄] is extracted from the residue with 10 ml of CH₃CN. Theorganic phase is evaporated in a rotary evaporator. The crude product iswashed with 10 ml of CH₂Cl₂ and dried under reduced pressure. Yield 0.25g (93%, 1.9 mmol).

According to DSC measurements, the salt decomposes above 300° C.

EXAMPLE 5 Trityl Tetracyanoborate, [Ph₃C][B(CN)₄]

500 mg (2.3 mmol) of Ag[B(CN)₄] and 726 mg (2.3 mmol) of (C₆H₅)₃CBr inanhydrous acetonitrile are brought to reaction in a 250 ml glass flaskwith PTFE valve (Young, London). The acetonitrile is removed underreduced pressure after 4 hrs, and 100 ml of dichloromethane aresubsequently added. The suspension is filtered through a Celite®-coveredfrit in a Schlenk flask. The reaction flask is rinsed twice withdichloromethane (20 ml and 10 ml). The solution is evaporated to 10 mlunder reduced pressure, and, after addition of 70 ml of anhydroushexane, an orange solid precipitates out. This is filtered off via aSchlenk frit and rinsed with a further 10 ml of hexane. The orange[Ph₃C][B(CN)₄] is dried under reduced pressure and stored in a dry box.The yield is 408 mg (51%, 1.3 mmol).

¹H-NMR: δ=7.73 ppm (m, 6H, o-H), δ=7.94 ppm (m, 6H, m-H), δ=8.31 ppm(tt, 3H, p-H); ¹³C{¹H}-NMR: δ=122.7 ppm (q, 4C, CN), ¹J(¹¹B,¹³C)=71.5Hz, δ=131.0 ppm (s, 6C, m-C), δ=140.2 ppm (s, 3C, i-C), δ=143.0 ppm (s,6C, o-C), δ=143.8 ppm (s, 3C, p-C), δ=211.2 ppm (s, 1C, C⁺); ¹¹B-NMR:δ=−38.6 ppm, ¹J(¹¹B,¹³C)=71.3 Hz; solvent: CDCl₃ reference substances:¹H- and ¹³C-NMR solvent signal (against TMS) and ¹¹B-NMR BF₃.Et₂O/CD₃CNas external standard

Results of the Elemental Analysis [Ph₃C][B(CN)₄]:

C [%] H [%] N [%] theoretical 77.12 4.22 15.64 found 77.19 4.21 15.50

[Ph₃C][B(CN)₄] melts at 158° C. with decomposition.

EXAMPLE 6 [HNPhMe₂][B(CN)₄]

1.50 g (9.7 mmol) of K[B(CN)₄] are dissolved in 50 ml of water. Firstly3 ml (36 mmol) of conc. HCl solution and subsequently 1.23 ml (9.7 mmol)of N,N-di-methylaniline are added to the solution with stirring,whereupon a white solid precipitates out. The solution is extractedtwice with dichloromethane (100 ml and 30 ml), the organic phase isdried using MgSO₄, and the dichloromethane is removed under reducedpressure, giving white [HNPhMe₂][B(CN)₄], which is purified by washingwith pentane. Yield 2.12 g (92%, 8.9 mmol).

¹H-NMR: δ=3.23 ppm (s, 6H, CH₃), ¹Δ¹H(^(12/13)C)=−0.0023, ¹J(¹H,¹³C)−145.48 Hz, δ=7.64-7.58 ppm (m, 5H, C₆H₅); ¹³C{¹H}-NMR: δ=47.8 ppm(s, 2C, CH₃), δ=121.5 ppm (s, 2C, C₆H₅), δ=123.2 ppm (s, 4C, CN),¹J(¹¹B,¹³C)=71.3 Hz, ¹Δ¹³C(^(10/11)B)=−0.0020 ppm, δ=131.5 ppm (s, 2C,C₆H₅), δ=131.6 ppm (s, 1C, C₆H₅), δ=143.1 ppm (s, 1C, C₆H₅); ¹¹B-NMR:δ=−38.6 ppm, ¹J(¹¹B,¹³C)=71.3 Hz; ¹⁵N-NMR: δ=−103.2 ppm (q, 4N, CN),¹J(¹¹B,¹⁵N)=0.73 Hz; solvent: CD₃CN; reference substances: ¹H- and¹³C-NMR solvent signal (against TMS), ¹¹B-NMR BF₃.Et₂O/CD₃CN as externalstandard and ¹⁵N-NMR 80% of CH₃NO₂ in CD₃CN as external standard.

Results of the Elemental Analysis of [HNPhMe₂][B(CN)₄]:

C [%] H [%] N [%] theoretical 60.80 5.10 29.54 found 60.60 4.65 28.50

[HNPhMe₂][B(CN)₄] melts at 101° C. and decomposes exothermically above246° C.

EXAMPLE 7 Tetraethylammonium Tetracyanoborate, [E4N][B(CN)₄]

7 g (46 mmol) of K[B(CN)₄] are dissolved in 300 ml of water and 8.4 g(46 mmol) of [Et₄N]Cl.H₂O are dissolved in 130 ml of water. The twosolutions are combined, whereupon a white solid precipitates oit. Afterstirring for 30 minutes, 250 ml of dichloromethane in which theprecipitated substance dissolves are added. The two phases areseparated, and the organic phase is dried over MgSO₄. Thedichloromethane is removed in a rotary evaporator, and the white solidis washed a number of times with pentane and subsequently dried underreduced pressure. Yield 10.5 g (96%, 43 mmol).

¹H-NMR: δ=1.22 ppm (tt, 12H, CH₃), ¹Δ¹H(^(12/13)C)=−0.0019 ppm,¹J(1H,¹³C)=128.78 Hz, ³J(1H¹,¹H)=7.27 Hz; δ=3.13 ppm (q, 8H, CH₂),¹Δ¹H(^(12/13)C)=0.0034 ppm, ¹J(¹H,¹³C)=144.30 Hz, ²J(¹H,¹⁴N)=1.89 Hz,³J(¹H,¹H)=7.28 Hz; ¹³C{¹H}-NMR: δ=7.8 ppm (s, 4C, CH₃); δ=53.2 ppm (t,4C, CH₂), ¹J(¹³C,¹⁵N)=3.1 Hz; δ=123.3 ppm (q, 4C, CN),¹Δ¹³C(^(10/11)B)=0.0021 ppm, ¹J(¹¹B,¹³C)=70.9 Hz; ¹¹B-NMR: δ=−38.6 ppm,¹J(¹¹B,¹³C)=71.2 Hz; solvent: CD₃CN reference substances: ¹H- and¹³C-NMR solvent peak (against TMS) and ¹¹B-NMR BF₃.Et₂O/CD₃CN asexternal standard.

Results of the Elemental Analysis of [E4N][B(CN)₄]:

C [%] H [%] N [%] theoretical 58.8 8.22 28.57 found 58.5 8.18 28.22

[E4N][B(CN)₄] melts at 230° C. A further reversible phase conversionoccurs at a temperature of 145° C. The salt decomposes above 360° C.

EXAMPLE 8 1-Butyl-3-methylimidazolium Tetracyanoborate [C₈H₁₅N₂][B(CN)₄]

0.35 g (2.3 mmol) of K[B(CN)₄] are dissolved in 20 ml of water. 0.53 g(3.0 mmol) of [C₈H₁₅N₂]Cl in 20 ml of water are added with stirring. Thesolution is extracted twice with dichloromethane (30 ml and 20 ml), theorganic phase is washed with water (20 ml) and dried using MgSO₄, andthe dichloromethane is subsequently removed under reduced pressure.Yield 0.50 g (87%, 2.0 mmol).

Results of the Elemental Analysis of [C₈H₁₅N₂][B(CN)₄]:

C [%] H [%] N [%] theoretical 56.70 5.95 33.07 found 56.24 6.13 32.99

[C₈H₁₅N₂][B(CN)₄] melts below −50° C. and decomposes endothermicallyabove 410° C.

EXAMPLE 9 1-Ethyl-3-methylimidazolium Tetracyanoborate [C₆H₁₁N₂][B(CN)₄]

[C₆H₁₁N₂][B(CN)₄] is prepared analogously to [C₈H₁₅N₂][B(CN)₄] with thesame yield.

Results of the Elemental Analysis of [C₆H₁₁N₂][B(CN)₄]:

C [%] H [%] N [%] theoretical 53.13 4.90 37.18 found 52.79 4.97 37.12

[C₆H₁₁N₂][B(CN)₄] melts below −50° C. and decomposes endothermicallyabove 420° C.

EXAMPLE 10 p-Methylbutylpyridinium Tetracyanoborate [C₁₀H₁₆N][B(CN)₄]

[C₁₀H₁₆N][B(CN)₄] is prepared analogously to [C₈H₁₅N₂][B(CN)₄] with thesame yield.

Results of the Elemental Analysis of [C₁₀H₁₆N][B(CN)₄]:

C [%] H [%] N [%] theoretical 63.42 6.08 26.42 found 62.81 6.13 26.70

[C₁₀H₁₆N][B(CN)₄] solidifies at −25° C., melts at 42° C. and decomposesendothermically above 390° C.

EXAMPLE 11 Preparation of K[BF₂(CN)₂]

Variant A: 5.88 g (41 mmol) of BF₃.OEt₂ and 30 ml of CH₃CN are condensedonto 4.12 g (63 mmol) of KCN in a 50 ml flask with PTFE valve. Thereaction mixture is stirred at room temperature for 3 h, and allvolatile constituents are subsequently removed under reduced pressure,and the residue is dissolved in about 50 ml of CH₃CN and freed from KCNand K[BF₄] by filtration. After removal of the acetonitrile underreduced pressure, 2.66 g (19 mmol) of K[BF₂(CN)₂] (¹¹B- and ¹⁹F-NMR: 93%of [BF₂(CN)₂]⁻, 0.3% of [BF₃(CN)]⁻ and about 7% of unknown species) areobtained. Yield: 92%. Pure colourless K[BF₂(CN)₂] is obtained byrecrystallisation from water. Isolated yield: 2.08 g (72%, 15 mmol).

Variant B: 65 g (1.0 mol) of KCN and 200 ml of CH₃CN are initiallyintroduced in a 500 ml round-bottomed flask with dropping funnel. 50 ml(56 g, 0.4 mol) of BF₃.OEt₂ are added dropwise over the course of halfan hour with stirring at room temperature. During the addition, thetemperature rises to 50° C. After further stirring (1.5 h) at roomtemperature, the solution is filtered off, and the filter residue (KCNand K[BF₄]) is washed with about 300 ml of CH₃CN. The combinedacetonitrile phases are evaporated in a rotary evaporator, giving 20 gof impure K[BF₂(CN)₂] as crude product. The crude product is reactedwith 30 ml of conc. HCl and 35 ml (25 g, 170 mmol) of tripropylamine in200 ml of water and extracted as tripropylammonium salt with 200 ml ofdichloromethane. The dichloromethane phase is dried using MgSO₄ andreacted with vigorous stirring with 25 g of KOH dissolved in as littlewater as possible. The viscous aqueous phase is separated off and washedwith dichloromethane. The product is extracted from the residue withabout 300 ml of CH₃CN, and the solution is dried using K₂CO₃ andevaporated in a rotary evaporator. The white product is washed withdichloromethane and dried under reduced pressure. Yield: 17 g (60%, 120mmol). According to ¹¹B-NMR, the substance contains 98% of [BF₂(CN)₂]⁻.

EXAMPLE 12 1-Ethyl-3-methylimidazolium Tricyanofluoroborate[C₆H₁₁N₂][BF(CN)₃]

[C₆H₁₁N₂][BF(CN)₃] is prepared analogously to [C₈H₁₅N₂][B(CN)₄] withyield.

Results of the Elemental Analysis of [C₆H₁₁N₂][BF(CN)₃]:

C [%] H [%] N [%] theoretical 49.35 5.06 31.98 found 48.52 4.84 31.20

[C₆H₁₁N₂][BF(CN)₃] is liquid at room temperature.

EXAMPLE 13 1-Butyl-3-methylimidazolium Tricyanofluoroborate[C₈H₁₅N₂][BF(CN)₃]

[C₈H₁₅N₂][BF(CN)₃] is prepared analogously to [C₈H₁₅N₂][B(CN)₄] yield.

Results of the Elemental Analysis of [C₈H₁₅N₂][BF(CN)₃]:

C [%] H [%] N [%] theoretical 53.47 6.12 28.34 found 54.06 6.09 28.68

[C₈H₁₅N₂][BF(CN)₃] melts below −50° C. and decomposes exothermicallyabove 300° C.

EXAMPLE 14 p-Methylbutylpyridinium Tricyanofluoroborate[C₁₀H₁₆N][BF(CN)₃]

[C₁₀H₁₆N][BF(CN)₃] is prepared analogously to [C₈H₁₅N₂][B(CN)₄] with thesame yield.

Results of the Elemental Analysis of [C₁₀H₁₆N][BF(CN)₃]:

C [%] H [%] N [%] theoretical 60.50 6.25 21.71 found 61.13 5.51 22.35

[C₁₀H₁₆N][BF(CN)₃] melts below −50° C. and decomposes exothermicallyabove 260° C.

EXAMPLE 15 1-Ethyl-3-methylimidazolium Dicyanodifluoroborate[C₆H₁₁N₂][BF₂(CN)₂]

[C₆H₁₁N₂][BF₂(CN)₂] is prepared analogously to [C₈H₁₅N₂][B(CN)₄] withthe same yield.

Results of the Elemental Analysis of [C₆H₁₁N₂][BF₂(CN)₂]:

C [%] H [%] N [%] theoretical 45.32 5.23 26.43 found 45.14 5.14 26.28

[C₆H₁₁N₂][BF₂(CN)₂] melts below −50° C. and decomposes exothermicallyabove 200° C.

EXAMPLE 16 1-Butyl-3-methylimidazolium Dicyanodifluoroborate[C₈H₁₅N₂][BF₂(CN)₂]

[C₈H₁₅N₂][BF₂(CN)₂] is prepared analogously to [C₈H₁₅N₂][B(CN)₄] withthe same yield.

Results of the Elemental Analysis of [C₈H₁₅N₂][BF₂(CN)₂]:

C [%] H [%] N [%] theoretical 50.03 6.30 23.34 found 50.20 6.31 23.42

[C₈H₁₅N₂][BF₂(CN)₂] melts below −50° C. and decomposes exothermicallyabove 210° C.

EXAMPLE 17 p-Methylbutylpyridinium Dicyanodifluoroborate[C₁₀H₁₆N][BF₂(CN)₂]

[C₁₀H₁₆N][BF₂(CN)₂] is prepared analogously to [C₈H₁₅N₂][B(CN)₄] withthe same yield.

Results of the Elemental Analysis of [C₁₀H₁₆N][BF₂(CN)₂]:

C [%] H [%] N [%] theoretical 57.40 6.42 16.74 found 57.70 6.20 16.95

[C₁₀H₁₆N][BF₂(CN)₂] melts below −50° C. and decomposes exothermicallyabove 190° C.

1. A process for the preparation of alkali metal cyanoborates of formula (1) M⁺[B(CN)₄]⁻  (1), where M is Li, Na, K, Rb or Cs, comprising reacting an alkali metal tetrafluoroborate M[BF₄], where M=Li, Na, K, Rb or Cs with an alkali metal cyanide MCN, where M=Li, Na, K, Rb, or Cs, in a solid-state reaction.
 2. The process according to claim 1, wherein the alkali metal tetrafluoroborate is K[BF₄] or Na[BF₄], and in that the alkali metal cyanide is KCN or NaCN.
 3. The process according to claim 1, comprising reacting the alkali metal tetrafluoroborate with the alkali metal cyanide in the presence of a lithium halide which is LiCl, LiBr or LiI.
 4. The process according to claim 3, wherein the alkali metal cyanide and the lithium halide are employed in the molar ratio 1:1.
 5. The process according to claim 1, wherein the alkali metal tetrafluoroborate and the alkali metal cyanide are employed in the molar ratio of 1:4 to 1:12.
 6. The process according to claim 1, wherein the alkali metal tetrafluoroborate employed is K[BF₄] and the alkali metal cyanide employed is KCN.
 7. The process according to claim 1, wherein reacting is carried out at temperatures between 100° C. and 500° C.
 8. A process for the preparation of alkali metal cyanoborates of formula (2) M⁺[BF_(n)(CN)_(4-n)]⁻  (2), where n=0, 1, 2 or 3 and M is Li, Na, K, Rb or Cs, comprising reacting an alkali metal cyanide MCN with boron trifluoride etherate BF₃OEt₂.
 9. The process according to claim 8, comprising reacting the alkali metal cyanide with the boron trifluoride etherate in the presence of an aprotic solvent.
 10. The process according to claim 9, comprising reacting the alkali metal cyanide with the boron trifluoride etherate in the presence of acetonitrile, diethyl ether, tetrahydrofuran and/or dimethoxyethane.
 11. The process according to claim 8, wherein the alkali metal cyanide is potassium cyanide KCN.
 12. The process according to claim 8, wherein the reaction is carried out at temperatures of −80 to 100° C.
 13. A process for the preparation of a salt of formula (3) Kt⁺[BF_(n)(CN)_(4-n)]⁻  (3), where n=0, 1, 2 or 3, and Kt⁺ is an organic cation, with the proviso that the cation Kt⁺ is not [N(C₄H₉)₄]⁺ for n=0, comprising reacting an alkali metal cyanoborate of formula M⁺[B(CN)₄]⁻, where M is Li, Na, K, Rb or Cs, prepared according to claim 1 with Kt⁺X⁻, where X is Cl, Br or I, and Kt⁺ is an organic cation, with the proviso that the cation Kt⁺ is not [N(C₄H₉)₄]⁺ for n=0.
 14. The process according to claim 13, wherein the organic cation Kt⁺ is

where R=H, with the proviso that at least one R on the nitrogen or phosphorous atom is different from H, straight-chain or branched alkyl having 1-20 carbon atoms straight-chain or branched alkenyl having 2-20 carbon atoms and one or more double bonds straight-chain or branched alkynyl having 2-20 carbon atoms and one or more triple bonds saturated, partially or fully unsaturated cycloalkyl having 3-7 carbon atoms halogen, with the proviso that no halogen-hetero atom bond is present, —NO₂, with the proviso that no bond to a positively charged hetero atom is present, and at least one R is different from NO₂, —CN, with the proviso that no bond to a positively charged hetero atom is present, and at least one R is different from CN, where the R are in each case identical or different, where the R may be bonded to one another in pairs by single or double bond, where one or more R may be partially or fully substituted by halogens, or partially by —CN or —NO₂, with the proviso that not all R are fully halogenated, and where one or two carbon atoms of the R may be replaced by hetero atoms and/or —O—, —C(O)—, C(O)O—, —S—, —S(O)—, —SO₂—, —S(O)₂O—, —N═, —P═, —NR′—, —PR′—, —P(O)(OR′)—, —P(O)(OR′)O—, —P(O)(NR′R′)—, —P(O)(NR′R′)O—, —P(O)(NR′R′)NR′—, —S(O)NR′— or —S(O)₂NR′—, where R′═H, non-, partially or perfluorinated C₁- to C₆-alkyl or non-, partially or perfluorinated phenyl.
 15. The process according to claim 13, wherein the organic cation Kt⁺ is


16. A salt of formula (3) Kt⁺[BF_(n)(CN)_(4-n)]⁻  (3) where n=1, 2 or 3, and Kt⁺ is an organic cation.
 17. The salt according to claim 16, wherein the organic cation Kt⁺ is

where R=H, with the proviso that at least one R on the N or P atom is different from H, straight-chain or branched alkyl having 1-20 carbon atoms straight-chain or branched alkenyl having 2-20 carbon atoms and one or more double bonds straight-chain or branched alkynyl having 2-20 carbon atoms and one or more triple bonds saturated, partially or fully unsaturated cycloalkyl having 3-7 carbon atoms halogen, with the proviso that no halogen-hetero atom bond is present, —NO₂, with the proviso that no bond to a positively charged hetero atom is present, and at least one R is different from NO₂, —CN, with the proviso that no bond to a positively charged hetero atom is present, and at least one R is different from CN, where the R are in each case identical or different, where the R may be bonded to one another in pairs by single or double bond, where one or more R may be partially or fully substituted by halogens, or partially by —CN or —NO₂, with the proviso that not all R are fully halogenated, and where one or two carbon atoms of the R may be replaced by hetero atoms and/or —O—, —C(O)—, C(O)O—, —S—, —S(O)—, —SO₂—, —S(O)₂O—, —N═, —P═, —NR′—, —PR′—, —P(O)(OR′)—, —P(O)(OR′)O—, —P(O)(NR′R′)—, —P(O)(NR′R′)O—, —P(O)(NR′R′)NR′—, —S(O)NR′— and —S(O)₂NR′—, where R′═H, non-, partially or perfluorinated C₁- to C₆-alkyl or non-, partially or perfluorinated phenyl.
 18. The salt according to claim 16, wherein the organic cation Kt⁺ is


19. A process for the preparation of a salt of formula (3) Kt⁺[BF_(n)(CN)_(4-n)]⁻  (3), where n=0, 1, 2 or 3, and Kt⁺ is an organic cation, with the proviso that the cation Kt⁺ is not [N(C₄H₉)₄]⁺ for n=0, comprising reacting an alkali metal cyanoborate of formula M[BF_(n)(CN)_(4-n)]⁻, where n=0, 1, 2 or 3 and M is Li, Na, K, Rb or Cs, prepared according to claim 8, with Kt⁺X⁻, where X is Cl, Br or I, and Kt⁺ is an organic cation, with the proviso that the cation Kt⁺ is not [N(C₄H₉)₄]⁺ for n=0.
 20. A salt of the following formula Kt⁺[B(CN)₄]⁻ where Kt⁺ is an organic cation of one of the following formulae

where R=H, with the proviso that at least one R on the N or P atom is different from H, straight-chain or branched alkyl having 1-20 carbon atoms straight-chain or branched alkenyl having 2-20 carbon atoms and one or more double bonds straight-chain or branched alkynyl having 2-20 carbon atoms and one or more triple bonds saturated, partially or fully unsaturated cycloalkyl having 3-7 carbon atoms halogen, with the proviso that no halogen-hetero atom bond is present, —NO₂, with the proviso that no bond to a positively charged hetero atom is present, and at least one R is different from NO₂, —CN, with the proviso that no bond to a positively charged hetero atom is present, and at least one R is different from CN, where the R are in each case identical or different, where the R may be bonded to one another in pairs by single or double bond, where one or more R may be partially or fully substituted by halogens, or partially by —CN or —NO₂, with the proviso that not all R are fully halogenated, and where one or two carbon atoms of the R may be replaced by hetero atoms and/or —O—, —C(O)O—, —S—, —S(O)₂O—, —N═, —P═, —NR′—, —P(O)(OR′)—, —P(O)(OR′)O—, —P(O)(NR′R′)—, —P(O)(NR′R′)O—, —P(O)(NR′R′)NR′—, —S(O)NR′— and —S(O)₂NR′—, where R′═H, non-, partially or perfluorinated C₁- to C₆-alkyl or non-, partially or perfluorinated phenyl, with the proviso that the cation Kt⁺ is not [N(C₄H₉)₄]⁺.
 21. A salt according to claim 20, wherein Kt⁺ is a cation of the following formula


22. A salt according to claim 20, wherein Kt⁺ is a cation of the following formula


23. A salt according to claim 20, wherein Kt⁺ is a cation of one of the following formulae 